The main constituent of guarana is caffeine, with smaller quantities of theophylline and theobromine. There is no evidence that the berries or extracts contain anything else that is therapeutically useful.Guarana is associated with many therapeutic properties, but there is no evidence to support these other than effects that can be attributed to caffeine. Guarana is widely available in herbal products and energy drinks. Excessive intake can cause the same effects as too much caffeine. It is not widely recognised that guarana has a high caffeine content and the labelling on some products is misleading.Although not specifically studied, guarana would be expected to exhibit the same range of adverse effects and drug interactions as those associated with caffeine.